Method and apparatus for marine wide azimuth towed steamer seismic acquisition

Abstract

This is a method of acquiring marine wide azimuth towed streamer seismic data. Preferably, a recording boat which tows a plurality of seismic streamers and at least one source may be accompanied by a plurality of source boats that each tow at least one source. The source boats may preferably activate their respective sources such that the subsurface reflections generated by each source interfere. The time separation between successive shots may preferably be a random variable related to the lowest frequency of interest in the data. Additionally, the source boats may preferably be alternatively fired from the head and tail of the recording streamers.

What is claimed is: 
     
       1. A method of seismic exploration, comprising:
 (a) positioning a seismic receiver boat at a location proximate a subsurface target, said seismic receiver boat pulling at least one seismic streamer therebehind, said at least one seismic streamer having a head end proximate to said receiver boat and a trailing end remote from said receiver boat; 
 (b) positioning a first seismic source proximate to either said head end of said at least one seismic streamers or said trailing end of said plurality of seismic streamers; 
 (c) positioning a second seismic source proximate an opposite end of said at least one seismic streamers from said first seismic source; 
 (d) activating said first seismic source; 
 (e) waiting a random length of time following said first seismic source activation and then activating said second seismic source, said random length of time being selected such that recorded seismic energy from said second source activation interferes with recorded seismic energy from said first source activation; 
 (f) continuously recording reflected seismic energy from said activation of said first seismic source and from said activation of said second seismic source via said at least one seismic streamer, thereby obtaining a plurality of seismic traces that record at least said first and second seismic source activations; 
 (g) performing at least (a) through (f) a plurality of times at a plurality of different locations proximate to said subsurface target while continuously recording, thereby obtaining a blended source seismic survey comprised of a plurality of source activations, wherein a sequence comprises said performing of at least (a) through (f) said plurality of times, said sequence comprising two or more activations of at least one of said first seismic source and said second seismic source; and, 
 (h) using said blended source seismic survey to explore for hydrocarbons within said region of the subsurface. 
 
     
     
       2. The method of seismic exploration according to  claim 1 , wherein there is a lowest frequency of interest in said blended source seismic survey and wherein said random length of time of (e) is chosen to be longer than a wavelength of said lowest frequency of interest in said blended seismic survey. 
     
     
       3. The method of seismic exploration according to  claim 1 , wherein said first source comprises a plurality of marine air guns. 
     
     
       4. The method of  claim 1 , wherein (h) comprises:
 (h1) selecting a particular source activation from among said plurality of source activations in said blended source seismic survey, 
 (h2) separating said selected source activation from said blended source seismic survey by using sparse inversion, thereby obtaining a single source gather, and, 
 (h3) using said single source gather to explore for hydrocarbons within said region of the subsurface containing structural or stratigraphic features conducive to the presence, migration, or accumulation of hydrocarbons. 
 
     
     
       5. The method of  claim 1 , wherein (h) comprises:
 (h1) selecting a particular source activation from among said plurality of source activations in said blended source seismic survey, 
 (h2) separating said selected source activation from said blended source seismic survey to obtain a single source gather by solving
   d=ΓS m,
 
 where, 
 d is said selected particular source activation, 
 m is said single source gather, 
 S is a matrix or operator that constrains m by requiring similarity between nearby source activations, and, 
 Γ is a blending matrix which describes at least an activation time of said particular source activation. 
 
 
     
     
       6. A method of seismic exploration, comprising:
 (a) in a computer, accessing a blended source seismic survey collected by a method comprising:
 (1) positioning a seismic receiver boat at a location proximate to a subsurface target, said seismic receiver boat pulling at least one seismic streamer therebehind, said at least one seismic streamer having a head end proximate to said receiver boat and a trailing end remote from said receiver boat; 
 (2) activating a first seismic source at a location proximate to said head end or said trailing end of said at least one seismic streamer; 
 (3) waiting a random length of time following said first seismic source activation and then activating a second seismic source at a location laterally offset from said at least one seismic streamer, said random length of time being selected such that seismic energy recorded by said at least one streamer from said second source activation interferes with recorded seismic energy from said first source activation; 
 (4) continuously recording reflected seismic energy from said activation of said first seismic source and from said activation of said second seismic source via said at least one seismic streamer, thereby obtaining a plurality of seismic traces that record at least said first and second seismic source activations; 
 (5) performing at least steps (1) through (4) a plurality of times at a plurality of different locations proximate to said subsurface region while continuously recording, thereby obtaining said blended source seismic survey, wherein a sequence comprises said performing of at least (1) through (4) said plurality of times, said sequence comprising two or more activations of at least one of said first seismic source and said second seismic source; and, 
 
 (b) using said blended source seismic survey to explore for hydrocarbons within subsurface region. 
 
     
     
       7. The method of seismic exploration according to  claim 6 , wherein there is a lowest frequency of interest in said blended source seismic survey and wherein said random length of time of (a)(3) is chosen to be longer than a wavelength of said lowest frequency of interest in said blended seismic survey. 
     
     
       8. The method of seismic exploration according to  claim 6 , wherein said first seismic source comprises a plurality of marine air guns. 
     
     
       9. The method of  claim 6 , wherein (b) comprises:
 (b1) selecting a particular source activation from among said plurality of source activations in said blended source seismic survey, 
 (b2) separating said selected source activation from said blended source seismic survey by using sparse inversion, thereby obtaining a single source gather, and, 
 (b3) using said single source gather to explore for hydrocarbons within said region of the subsurface containing structural or stratigraphic features conducive to the presence, migration, or accumulation of hydrocarbons. 
 
     
     
       10. The method of  claim 6 , wherein step (b2) comprises:
 (i) selecting a particular source activation from among said plurality of source activations in said blended source seismic survey, 
 (ii) separating said selected source activation from said blended source seismic survey to obtain a single source gather by solving
   d =ΓS m,
 
 where, 
 d is said selected particular source activation, 
 m is said single source gather, 
 S is a matrix or operator that constrains m by requiring similarity between nearby source activations, and, Γ is a blending matrix which describes at least an activation time of said particular source activation. 
 
 
     
     
       11. A method of seismic exploration, comprising:
 (a) positioning a seismic receiver boat at a location proximate a subsurface target, said seismic receiver boat pulling at least one seismic streamer therebehind, said at least one seismic streamer having a head end proximate to said receiver boat and a trailing end remote from said receiver boat; 
 (b) positioning a first seismic source proximate to either said head end of said at least one seismic streamers or said trailing end of said plurality of seismic streamers; 
 (c) positioning a second seismic source laterally offset from said first seismic source, the first and second seismic source forming a first pair; 
 (d) activating said first seismic source; 
 (e) waiting a random length of time following said first seismic source activation and then activating said second seismic source, said random length of time being selected such that recorded seismic energy from said second source activation interferes with recorded seismic energy from said first source activation; 
 (f) continuously recording reflected seismic energy from said activation of said first seismic source and from said activation of said second seismic source via said at least one seismic streamer, thereby obtaining a plurality of seismic traces that record at least said first and second seismic source activations; 
 (g) performing at least steps (a) through (f) a plurality of times at a plurality of different locations proximate to said subsurface target while continuously recording, thereby obtaining a blended source seismic survey comprised of a plurality of source activations, wherein a sequence comprises said performing of at least (a) through (f) said plurality of times, said sequence comprising two or more activations of at least one of said first seismic source and said second seismic source; and, 
 (h) using said blended source seismic survey to explore for hydrocarbons within said region of the subsurface. 
 
     
     
       12. The method of  claim 11 , further comprising:
 positioning one or more additional pairs of seismic sources proximate to the seismic receiver boat, wherein each additional pair of seismic source comprises a first seismic source and a second seismic source; and 
 activating the one or more additional pairs of seismic sources after (e). 
 
     
     
       13. The method of  claim 12 , wherein the first and second seismic sources in the one or more additional pairs are laterally offset from one another. 
     
     
       14. The method of  claim 12 , wherein the activating the one or more pairs comprises, for each additional pair of seismic sources, waiting a random length of time following activation of the first seismic source in the one more additional pairs and then activating the second seismic source in the one or more additional pairs, said random length of time being selected such that recorded seismic energy from each said second source activations interferes with recorded seismic energy from each of said first source activations. 
     
     
       15. The method of  claim 14 , wherein the random length of time comprises a pseudo-random length of time. 
     
     
       16. The method of  claim 11 , wherein the first seismic source and the second seismic source each comprises an air gun, a vibrator, a resonator, a siren, or combinations thereof. 
     
     
       17. A method of seismic exploration, comprising:
 (a) positioning a seismic receiver boat at a location proximate a subsurface target, said seismic receiver boat pulling at least one seismic streamer therebehind, said at least one seismic streamer having a head end proximate to said receiver boat and a trailing end remote from said receiver boat; 
 (b) positioning a first seismic source proximate to either said head end of said at least one seismic streamers or said trailing end of said plurality of seismic streamers; 
 (c) positioning a second seismic source proximate an opposite end of said at least one seismic streamers from said first seismic source; 
 (d) activating a first source; 
 (e) waiting a random length of time following said first source activation and then activating a second source, said random length of time being selected such that recorded seismic energy from said second source activation interferes with recorded seismic energy from said first source activation, wherein said first source comprises said first seismic source or said second seismic source and said second source comprises said first seismic source or said second seismic source; 
 (f) continuously recording reflected seismic energy from said activation of said first source and from said activation of said second source via said at least one seismic streamer, thereby obtaining a plurality of seismic traces that record at least said first and second source activations; and 
 (g) performing at least (a) through (f) a plurality of times at a plurality of different locations proximate to said subsurface target while continuously recording, thereby obtaining a blended source seismic survey comprised of a plurality of source activations, wherein a sequence comprises said performing of at least (a) through (f) said plurality of times, said sequence comprising two or more consecutive activations of at least one of said first seismic source and said second seismic source.